Production of columbium containing steels



rates Patent 3,102,831 Patented Sept. 3, 1963 3,102,831 PRODUCTION OF COLUMBIUM CONTAINING STEELS Norman F. Tisdale, Pittsburgh, Pa., assignor to Molybdenum Corporation of America, New York, N.Y., a corporation of Delaware No Drawing. Filed Aug. 10, 1960, Ser. No. 48,587 6 Claims. (Cl. 148-i2) The present invention provides a novel and improved process for the production of colurnbium containing steels having improved properties. More particularly, it relates to the production of rolled sheets, plates, bars and tubes, and includes correlated improvements and discoveries whereby the properties of steels are decidedly improved.

An object of the present invention is to provide a process in accordance with which a steel maybe produced having a line grain, With improved physical properties, such as yield strength and low temperature impact strength, in the ans-rolled condition.

A particular object of the invention is the provision of a process whereby steels may be produced through the utilization of columbium, for example as elemental columbium or in the form of an alloy such as ferrocolumbium, preferably having a low melting point which suitably is substantially equal to or lower than the temperature of the steel melt in the ladle. Also, there may be utilized a composition containing columbium oxide with a reducing agent.

The improved process of the present invention may be used with rimmed, killed and semi-killed steels of alloy and of carbon grades, and the steel may be manufactured by procedures which involve no unusual steps.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

It has been shown that small amounts of colum bium will enhance the tensile strength and yield point of steel in the as- -rolled condition but usually unless certain additional steps are resorted to there will also result an increase in embrittlement temperature which for many purposes reduces the value of the steel. This is even more markedly true in the use of oolumbium in excess of 0.015%. I have found that the use of columbium, and within a definite range, combined with the judicious use of silcon, carhot: and manganese and proper temperature processng according to the present invention, can produce a steel with high tensile properties and with embrittlement temperatures which render the steel useful in a wide variety of applications.

The process of the present invention especially avoids adversely affecting the low temperature transverse impact properties of colurnbium steels prepared according to convcntional produces, retaining the fine grain, While also resisting grain growth at elevated temperatures.

The process of the present invention is also highly advantageous in that it produces semidcilled, killed or rimmed steels which have exceptionally good properties in the as-rolled" condition, and yet may be subjected to further heat treatment to develop other desirable physical properties.

The process of the present invention also avoids the relatively poor ductilit high transition temperatures and low impact values which characterize conventional columbium containing rolled steels which have been made by the usual processes, and which generally contain small en velopes of columbium carbide especially around the grain boundaries.

The invention accordingly comprises the several steps and the relation of one or more of such steps with relation to each of the others which are exemplified in the following detailed disclosure and the scope of the invention will be indicated in the claims.

In the practice of the invention, the properties of rimmed, killed or semi-killed steels are decidedly improved by the addition of an appropriate and definite amount of columbium suitably in the form of a self-reducing mixture of columbium oxide and a reducing agent or an alloy with iron, namely, a lerrocolumbiurn, and preferably with an alloy which has a melting point which is substantially equal to or lower than the temperature of the steel melt in the ladle.

The amount of the columbium may vary from about 0.005% to about 0.050% based on the weight of the melt. More desirably, it may be in an amount of from 0.015% to 0.037% for either semi-killed, killed or rimmed steels. The composition of the fcrro-columbium may be from about 81% to 25% iron and from about 19% to about of columbiurn. Advantageously, the percentage of iron may be about 50% and the amount of columbium about 43% with about 7% impurities.

In general, the analyses of the columbium-containing steels for use with the present invention show a carbon content of 0.02% to 0.50%, silicon from 0.005% to 0.5%, manganese from 015% to l.6% and colurnbium from 0.005% to 0.050%. The following tables show more particular analysis ranges for semi-killed, killed and rimmed steels:

Semi-Killed Steels Carbon 0.04 to 0.40%, preferably 0.15

to 0.25%. Silicon 0.005 to 0.1%, preferably 0.01

to 0.1%. Manganese 0-60 to 1.6%, preferably 0.85

to 1.20%. Columbium 0.005 to 0.050%, preferably 0.015 to 0.30%. Phosphorus and sulfur impurities in normal amounts.

Killed Steels 0.015 to 0.030%. Phosphorus and sulfur impurities in normal amounts.

Rimmed Steels Carbon 0.005 to 0.02%.

Silicon 0.005 to 0.02%.

Manganese 0.15 to 060%, preferably 0.25

Columbium 0.005 to 0.050%, preferably 0.015 to 0.030%. Phosphorus and sulfur impurities in normal amounts.

More especially, the procedure comprises preparing a steel melt, adding thereto when the steel is ready either during furnacing or to the ladle or to the ingot mold, a columbium containing material having a melting point substantially not higher than the temperature of the melt. More particularly, the colurnbium containing material may be in the form of an alloy, e.g., a ferro-eolurnbium, having the melting point as above indicated, or as a selfreducing mixture containing columbiurn oxide.

F urthermorc, the coiumbium may be added to the ingot mold and in an effective amount not more than about 1.0 pound of colurnbium per ton of steel. Additionally, the addition of the columbium may be partially in the furnace and partially in the ladle, or in the ingot mold. If desired, the melt may be deoxidized at a suitable stage in the manufacture through the utilization, e.g., of ferrosilicon, calcium, silicon, form-manganese, and the like. The addition of the columbium containing material may be effected at different phases of the melting and furna-cing and in any convenient and effective manner.

The columbium material may be added to the ingot mold or partly to the furnace and partly to the mold. I have found that when about 0.1 to 1.0 pounds of columbium per ton of steel have been added, there may be ob tained a fine grain structure attended by distinct unifiOrmity and resulting in a product which has outstanding physical and working qualities and properties. Furthermore, I have found that depending on the pouring temperature, the size of the mold and the analysis of the steel desired, an amount of about 0.8 pound or slightly less columbium to the ton has accorded beneficial results.

The ingots, slabs or bars prepared as above, and including from 0.015% to 0.030% columbium are heated in heating furnaces, prior to rolling, and are soaked for a period of from 7 to hours at a temperature of from about 2300" F. to 2450 F. after which it is rolled to the desired finished size.

After or during rolling, and while the temperature of the steel remains relatively high, between 1550 and 1750 F., it is subjected to rapid cooling to reduce its temperature rapidly to under 1300", and preferably to less than 1100 or 1200 F. as by spraying it with water, after which it is allowed to air-cool at a normal rate.

Where tubes are being formed by rolling, the rapid cooling from the elevated temperature of 1550 to 1750 F. may be accomplished by using a cold steel mandrel or plug on the interior of the tube While it is rolled, thereby rapidly cooling the tube to a temperature of less than 1200 F. and preventing the precipitation of columbium carbide, especially at the grain boundaries.

The procedure described herein makes effective use of the columbium containing material suitably in the form of a ferro-columbium and at the same time utilizes a relatively small amount thereof. Accordingly, I have found that not more than 0.8 pound of eolumbium per ton should be used, although as little as 0.1 or 0.2 pound has a beneficial result.

Hence, the addition of columbium to such steels, or to a steel built around columbium addition, produces a better low alloy high strength steel, which processes without difficulty and which can be utilized as Well as the others.

The requirements for ship plate are certain tensile properties plus a low embrittlement temperature, and these are usually obtained by producing steel in a hot-top variety and then normalizing. Production of this steel by the semi-killed process leads to a greater yield and elimination of normalizing gives a lower cost steel.

The addition of 0.030% columbium to ship plate steel, I have found, raises the yield point and lowers the emhrittlement temperature. Furthermore, a small amount of columbium lowers the required carbon and manganese thereby lowering the embrittlement temperature and maintaining the tensile strength.

I have found that when columbium is added to a steel Steel analysis it accomplishes a fine grain; produces an increase in the tensile properties, and when added to a killed steel the recovery percentage is as much as 96.00%. Moreover, it does not form internal seams and, therefore, does not add an extra hazard to the grinding and polishing of the steel. Further, only a small amount is required, viz, from about 0.015% to about 0.030% or even from 0.005% to 0.050%.

Columbium added to low carbon steels (e.g., carburized grades and in amounts from about 0.015% to about 0.03 0% produces a very fine grain which persists at high temperature. It allows a higher carburizing temperature thus reducing the time required, and producing a steel lower in cost.

According to the process of the present invention, an ingot of semi-skilled or rimmed steel having from 0.005% to 0.050% columbiurn is soaked for 7 to 10 hours at a temperature of from 2300 to 2450 F., the time of soaking depending on the size of the ingot. For an ingot weighing about 25 tons and measuring about 32 by 66 by inches normally requires about 8 hours to attain a uniform temperature in the range of 2300 to 2450 F.

The ingot is then rolled in accordance with conventional procedure, and when finished has a temperature of from l550 to 1750 F., and is often heated one or more times during the finishing operation, so as to maintain a good rolling temperature.

When the finishing operation has been completed, the steel is immediately subjected to a heavy water spray so as to reduce its temperature from about 1550 to 1750 F. to a temperature in the range of 1050" to 1200" F., below the AC3 critical points, after which the steel is allowed to cool in air at a normal rate of cooling.

While the water-spray for rapidly reducing the temperature of the steel ordinarily begins at the conclusion of the finishing operation, the spraying may be begun at an earlier time and as soon as the temperature of the steel has been reduced to about 1800" F.

The foregoing procedures may be employed for the production of semi-killed, killed and rimmed steels, and enables the producers to take advantage of the extra production yield obtained from semi-killed over that of killed steels. I have noted that the increase in embrittlement temperature is of a very low order if the columbium is under 0.02%, but rises rapidly as this amount is exceeded unless the columbium containing steel is rapidly cooled, as by the water spray, from the range of 1550 to 1750 F. to the lower range of 1050 to 1200 F.

The data in the following table shows the transverse impact values obtained from several different steels which had been finished at approximately 1650 F. for 8 hours prior to rolling, and which had also been sub jeoted to water spray cooling to cause them to cool rap- F idly from about 1600 to about 1200 R, after which they are air-cooled at a normal rate.

Finish Transverse impact Gauge, temp, Water spray, inches 1. F.

M 1, 590 1,590 to 1,100. 35 35 30 V 1,090 1,690 to 1,200 22 20 18 A 1, 600 No H 18 15 7 ii 18 I8 17 1, 600 No J 7 5 .7

M 1, 600 No 20 16 8 M 1, 600 No 24 21 1D A 1, 590 1,800 to 1,2001- 35 35 30 4 l, 650 1,650 to 1,000. c 28 24 20 )4 1, 050 1,650 to 1,150. s11 51 52 1,580 1,580 to l,l00 20.5 14.5

l Semi-killed steel. 1 Rimmed steel.

The following examples snow the improvement in yield strength achieved by the addition of 0.03% columbium to a semi-killed steel, and by treatment of the steel after rolling with a water spray to reduce its temperature rapidly from about 1700 F. to about 1100 F.

(Specimen had a two-inch round section.)

Another comparison of specimens of a semi-killed steel in a /4" round bar, had the following analyses and properties:

Carbon, Mnn- Silicon, C olum- Yield percent ganesc, percent hium, strength percent percent 0. 36 l. 55 0. 22 0. 036 85, 300 l}. 36 1.55 0. 22 0 09, E00

Another comparison of specimens of a killed steel in a 1% inch bar, had the following analyses and properties:

Carbon, Mam Silicon, Colum- Yield percent. ganese, percent b nm, strength percent percent The invention in its broader aspects is not limited to the specific mechanisms shown and described but departures may be made therefrom within the scope of the accompanying claims without departing from the principles of the invention and without sacrificing its chief advantages.

Having described my invention, What I claim as new and desire to secure by Letters Patent is:

I. A method for the production of steels which cornprises preparing a steel ingot containing from 0.005% to 0.050% of columbium, on a Weight basis, heating the ingot prior to rolling to a temperature of at least 2300" F. until the ingot is uniformly heated to a temperature from about 2300 to 2450 F, rolling the ingot so that when finished it has a temperature of from about 1550 to 1750 F., and subjecting the ingot to a water spray to rapidly cool the rolled steel from th finishing temperature 6 range of 1550 to 1750 F., to a temperature range of 1050 to 1200 F.

2. A method for the production of steels which comprises preparing a steel ingot containing, on a weight basis, from 0.02% to 0.40% carbon, 0.005% to 0.5% silicon, 0.15% to 1.6% manganese and from 0.005% to 0.050% columbium, heating the ingot prior to rolling to a temperature of at least about 2300 F. until the ingot is uniformly heated to a temperature between about 2300 and 2450 F., rolling the ingot so that when it is finished it has a temperature of from about 1550" F. to i750 R, and subjecting the ingot to a water spray to cool it rapidly from a temperature exceeding 1550 F. to a temperature below 1200 F.

3. A method as claimed in claim 2 in which the steel is a semi-killed steel and includes, on a Weight basis, 0.005% to 0.050% columbium from 0.l0% to 0.40% carbon, 0.01% to 0.1% silicon and from 0.60% to 1.6% manganese.

4. A method as claimed in claim 2 in which the steel is a rimmed steel and includes, on a weight basis, 0.005% to 0.050% colurnbiurn, from 0.02% to 0.15% carbon, 0.005% to 0.02% silicon and from 0.15% to 0.60% manganese.

5. A method as claimed in claim 2 in which the steel is a killed steel and includes, on a weight basis, 0.005% to 0.050% columbium, from 0.04% to 0.60% carbon, 0.15% to 0.50% silicon, and 0.5% to 1.6% manganese.

6. A method as claimed in claim 2 in which the water spray is started While the steel is at a temperature of about 1800" F. and is continued until the steel is at a temperature of about 1050 F.

References Cited in the file of this patent UNITED STATES PATENTS 2,264,355 Becket et a1 Dec. 2, 1941 2,377,922 Campbell et a1 June 12, 1945 2,999,749 Saunders et al Sept. l3, 1961 3,010,822 Altenburger et al Nov. 28, 1961 FOREIGN PATENTS 755,444 Great Britain Aug. 22, 1956 OTHER REFERENCES The Making, Shaping and Treating of Steel, 7th Edition, pages 393498, 589-594; 1957.

Bray: Ferrous Production Metallurgy, pages 77 and 80, John Wiley 8: Son, 1942.

Metals Handbook, published by the American Society for Metals, 1948, page 352 relied upon. 

1. A METHOD FOR THE PRODUCTION OF STEELS WHICH COMPRISES PREPARING A STEEL INGOT CONTAINING FROM 0.005% TO 0.050% OF COLUMBIUM, ON A WEIGHT BASIS, HEATING THHE INGOT PRIOR TO ROLLING TO A TEMPERATURE OF AT LEAST 2300*F. UNTIL THE INGOT IS UNIFORMLY HEATED TO A TEMPERATURE FROM ABOUT 2300* TO 2450*F., ROLLING THE INGOT SO THAT WHEN FINISHED IT HAS A TEMPERATURE OF FROM ABOUT 1550* TO 1750*F., AND SUBJECTING THE INGOT TO A WATER SPRAY TO RAPIDLY COOL THE ROLLED STEEL FROM THE FINISHING TEMPERATURE RANGE OF 1550* TO 1750*F., TO A TEMPERATURE RANGE OF 1050* TO 1200*F. 